1. Field of the Invention
The invention concerns a method for parallax-free image acquisition of a two-dimensional, x-ray projection image of a predetermined projection region of a subject (in particular a patient) with a C-arm system, wherein the projection region of the subject that is to be imaged is larger than the maximum projection region between focus and detector that is covered by a stationary x-ray beam, and wherein at least two such individual rejection exposures are created and combined to generate a complete exposure of the entire projection region of the subject that is to be imaged.
Furthermore, the invention concerns a C-arm x-ray system, in particular mobile C-arm system having a C-arm that can be rotated automatically and moved in translation, with a radiation source with a focus being mounted at one end of the C-arm and a flat panel detector being mounted at the other end, wherein a control and computer system is connected with the C-arm system for automatic control of the C-arm and for image generation from acquired detector data.
2. Description of the Prior Art
C-arm systems as well as methods to generate projection exposures of the above general type are known and are frequently used in clinical applications for diagnosis and therapy support. The size of the flat panel detector that is used is limited, in particular in the mobile embodiment of such systems. For example, flat panel detectors with approximately 9-inch diagonals are presently used, from which results (dependent on the acquisition geometry) a projected field of view (image field) with less than 20 cm diagonals at or in the patient. Although this is sufficient in order to image individual smaller organs or bones, neither a complete lung exposure nor a complete pelvis exposure can be generated.
Furthermore, to solve this problem it is known in practice to acquire multiple x-ray images in the same acquisition geometry but with different perspectives (thus with a C-arm shifted in parallel), and assemble these individual exposures into a complete image. It is inherent to C-arm systems that, due to their structural support, the C-arm can execute only orbital rotations, rotations around a horizontal axis through the orbital plane, linear translations and what is known as a swivel motion (rotation around the vertical C-arm column). The multiple individual exposures acquired to cover a larger region to be imaged are normally executed by linear displacement of the acquisition system. However, the disadvantage hereby results that the complete exposure that is created from this procedure is a combination of individual images that were projected with the same (relatively small) projection angle but from different starting points (thus different focus positions), and therefore the assembled image does not give the natural impression of a single exposure with a large projection angle. A parallax error is thus created.